The Platelet-Activating Factor (PAF) is a biologically active phospholipid involved in physiological and pathophysiological processes. This factor is converted to biologically inactive products by a specific acetyl hydrolase, i.e. Platelet-Activating Factor Acetylhydrolase (PAF-AH, EC 3.1.1.47, also referred to as lipoprotein-associated phospholipase A2), which cleaves off the acetate group at the sn-2 position. In addition to PAF, the substrate specificity also comprises oxidized phospholipids having polar substituents at the ω-position of the sn-2 ester. These altered substances are often found in oxidized lipoproteins. Since oxidized lipoproteins, in addition to PAF and oxidized phospholipids, also play a role in a great variety of diseases, it may be assumed that the enzyme also has a decisive influence on the genesis of said diseases.